Method for the production of a metal tube, in particular a gas distributor tube for vehicle airbags

ABSTRACT

The invention relates to a method for the production of a metal tube, particularly a gas distributor tube for vehicle airbags. The tube mantle is punched out as a planar metal blank, the outside contour of which corresponds to the developed view of the tube. The planar metal blank is then formed into a profile having a U-shaped cross-section. The U-shaped profile is pressed to form a tube-shaped semi-finished piece that still has an open longitudinal slit. The longitudinal slit, which extends without interruption with an essentially constant gap width over the entire length of the tube, is finally welded closed. In the production of gas distributor tubes, the outside contour of the metal blank corresponds to a developed view of the gas distributor tube, whereby the parting plane for the developed view is laid through the exit openings.

The invention relates to a method for the production of a metal tube,which has at least one reduction in cross-section. According to anotherembodiment, the tube can contain functional elements, e.g. filterinserts, flow baffles, and the like. The invention specifically alsorelates to a method for the production of a gas distributor tube,particularly for vehicle air bags, which has a connector cuff, at leastone ring-shaped collar, and exit openings on the mantle, which are in arow in the longitudinal direction.

Gas distributor tubes that are used for head and side airbags invehicles, for example, are long, slim tubes having a plurality of exitopenings arranged in the longitudinal direction. The tubes have aconnector cuff for a connection to a gas source, as well as a collar, onwhich an inflatable bag is secured to prevent it from slipping off.Within the scope of the known measures, the exit openings are made inpre-finished tubes that have been cut to size, by means of punching themout. For this purpose, a mandrel has to be introduced into the tube. Anychips and punched parts that occur during the processing must becarefully removed, since even small particles can penetrate the suddenlyinflating bag when the airbag deploys. In other processing steps, thering-shaped collar is formed by means of compression, and the connectorcuff is pressed on and crimped. The production method is complicated.The complete removal of all particles and chips from the tube is also aproblem. Due to disruptions in the process, it is not always assuredthat the collar possesses the dimensions and shape that are required forreliable functioning of the gas distributor tube. In order to ensurethis, an enormous inspection effort is required.

The invention is based on the task of indicating a production methodwith which a tube that has changes in cross-section can be produced in asingle piece. In this connection, the production of tubes into whichfunctional elements have been firmly integrated or which have exitopenings on the mantle, as gas distributor tubes, and are suitable forvehicle airbags, is also supposed to be possible.

The object of the invention and the solution for this task is a methodfor the production of a metal tube, which has at least one change incross-section, whereby

-   -   the tube mantle is punched out as a planar metal blank, the        outside contour of which corresponds to the developed view of        the tube,    -   the planar metal blank is formed into a profile having a        U-shaped cross-section,    -   the U-shaped profile is pressed to form a tube-shaped        semi-finished piece that still has an open longitudinal slit,        and    -   the longitudinal slit, which extends without interruption with        an essentially constant gap width over the entire length of the        tube, is welded closed.

The longitudinal slit of the tube-shaped semi-finished piece can be usedfor aligning the work piece in a longitudinal welding machine, or toalign the welding tool on the work piece. The ends of the mantle thatare to be joined with one another are pressed together and welded.

The metal blank has segments of different width, which are connected bymeans of constant transition segments. According to a preferredembodiment of the invention, the metal blank is punched out in a widththat corresponds to the outside diameter of the tube, multiplied by thenumber π. Since the outside diameter of the tube to be produced, not theneutral phase in the tube mantle, is used as the basis for sizing thewidth of the blank, this results in a slight excess dimension, which isadvantageous during the subsequent welding of the longitudinal tubeseam, and contributes to the production of defect-free longitudinalseams.

Press die-plates configured as half-shells can be used for theproduction of the tube-shaped semi-finished piece. It is practical ifthe shank ends of the U-shaped profile are held at a distance that formsthe longitudinal slit, by means of a tongue, during the shaping. Awelding tool can be guided along the longitudinal slit of thetube-shaped semi-finished piece, which follows the contour of the tubeand welds the longitudinal seam of the tube closed.

The method according to the invention is furthermore suitable forproducing a tube with functional elements firmly integrated into it.Functional elements can be flow baffles, filter elements, static mixers,and similar components. Within the course of the deformation of themetal blank, functional elements are inserted, which are fixed in placewith a positive lock after completion of the tube. On the lengthwisesides of the planar metal blank, projections are formed, which form anannular space for holding the functional element, after deformation toproduce a tube-shaped semi-finished piece. If necessary, the contourforming the annular space can be finished with external shaping tools.According to a preferred embodiment of the invention, projections areformed on the lengthwise sides of the metal blank, which form abead-shaped widened tube region to hold a disk, after deformation toproduce a tube-shaped semi-finished piece. This widened tube region ispressed to form a collar, using shaping tools, in which the related diskis fixed in place with a positive lock.

Another embodiment of the method according to the invention providesthat a flow insert arranged between two support disks is laid into theprofile within the course of the deformation process, and that thesupport disks are fixed in place, with a positive lock, in beads thatare formed during the course of the deformation of the metal blank, andfinished using shaping tools.

According to another preferred embodiment of the invention, which isparticularly suitable for the production of gas distributor tubes, thelengthwise edges of the metal blank have a profile with back-sets, whichcomplement one another during the deformation of the metal blank, toform exit openings on the mantle, which are in a row in the longitudinaldirection.

It is practical if the profiles of the lengthwise sides of the metalblank also have projections from which a collar and a connector cuff areformed during the deformation of the metal blank to form a tube.

The metal blank can have a segment with a lesser width, which forms anarrowed cross-section of the tube after deformation of the metal blank.

Gas distributor tubes that are used in head or side airbags of vehicleshave a length that frequently amounts to between 1 m and 2 m. Accordingto a preferred embodiment of the invention, the metal blank used for theproduction of the tube is punched out of a piece of sheet metal, insegments, whereby the length of the segments is selected to be such thatthe transitions lie in the region of the back-sets on the edges of themetal blank that form the exit openings. Inaccuracies at thesetransitions are harmless, since no weld seam has to be formed in theregion of the exit openings.

In a final work step, the tube that has been produced from the planarmetal blank and welded longitudinally can be given a predeterminedspatial progression adapted to the application, by means of bending.

Alternatively, a bending deformation that shapes the work piece in thelongitudinal direction can take place at the same time with thedeformation of the metal blank and/or during the subsequent pressing toform a tube-shaped semi-finished piece. In this way, the work piece isgiven a spatial progression adapted to the application, before thelongitudinal slit of the tube-shaped semi-finished piece is weldedclosed. Preferably, the metal blank is deformed into a work piece havinga U-shaped cross-section, by means of bending in a forging die or edgerolling, which piece is curved in the longitudinal direction andsubsequently pressed into a tube shape using press die-plates, theshaping cavity of which is adapted to the shape of the work piece.

The work piece is already given a spatially curved progression duringthe deformation of the metal blank and/or during the subsequent pressingprocess to form a tube-shaped semi-finished piece, which is adapted tothe later use of the tube, e.g. as a gas distributor tube. Subsequentbending of the finished, welded tube is not required, or at least can berestricted to segments that are very greatly curved. The methodaccording to the invention particularly does not preclude thepossibility that segments curved in arc shape, for example, are deformedsubsequently, by means of bending of the tube that has already beenshaped three-dimensionally and welded at the longitudinal seam.

In the following, the invention will be explained using a drawing thatrepresents merely an exemplary embodiment. The drawing schematicallyshows:

FIG. 1 a metal tube produced according to the invention, in a side view,

FIG. 2 a metal blank for the production of the tube shown in FIG. 1,

FIG. 3 a first deformation of the metal blank shown in FIG. 2, to form aU-shaped profile,

FIG. 4 a second deformation step for the production of a tube-shapedsemi-finished piece made from the intermediate product shown in FIG. 3,

FIG. 5 a metal tube produced according to the method according to theinvention, with integrated functional elements,

FIG. 6 a preferred embodiment of the metal tube produced according tothe invention, having exit openings on the mantle, in a row in thelongitudinal direction, which can be used as a gas distributor tube fora vehicle airbag,

FIG. 7 a metal blank for the production of the gas distributor tubeshown in FIG. 6,

FIG. 8 a a curved gas distributor tube produced according to theinvention, for a vehicle airbag, in a side view,

FIG. 8 b a top view of the object of FIG. 8 a,

FIG. 9 another embodiment of a gas distributor tube produced accordingto the method according to the invention.

The tube 1 shown in FIG. 1 has changes in cross-section, e.g. for aconnector cuff 2 as well as for a ring-shaped collar 3.

The mantle for the metal tube shown in FIG. 1, having changes incross-section, is punched out as a planar metal blank 4. The metal blank4 is shown in FIG. 2. Its outside contour corresponds to the developedview of the tube 1. The width of the metal blank results from theoutside diameter of the tube multiplied by the number π. With referenceto the neutral phase running in the wall of the mantle, there is aslight excess dimension, which promotes the subsequent defect-freelongitudinal welding of the tube.

In a first deformation step, shown in FIG. 3, the metal blank 4 isdeformed to produce a profile 5 having a U-shaped cross-section.Subsequently, the U-shaped profile 5 is inserted between two die-plates6, 6′ of a press, which are configured as half-shells, and pressed toform a tube-shaped semi-finished piece 7, which has a cross-sectionprogression that corresponds to the tube 1, and a longitudinal slit thatis still open. From FIG. 4, it is evident that during this shaping, theshank ends of the U-shaped profile are held at a distance that forms thelongitudinal slit, by means of a tongue 8 that is inserted into thedie-plate 6.

The longitudinal slit of the tube-shaped semi-finished piece issubsequently welded closed, preferably by means of laser welding. Inthis connection, the welding tool can be guided along the longitudinalslit.

The method is also suitable for the production of a tube into whichfunctional elements 9 are firmly integrated. In the case of an exemplaryembodiment shown in FIG. 5, a flow insert 9, e.g. in the form of astatic mixer, is arranged within the tube 1 and fixed in place betweenring disks 10, as a functional element. The ring disks 10 are fittedinto collars 11 of the tube 1 that are formed in the mantle side, with apositive lock. The production of the tube 1 takes place in the mannerdescribed above. First, a planar metal blank is punched out, the outsidecontour of which corresponds to the developed view of the tube and hasprojections for forming bead-shaped widened regions of the tube. Thering disks 10 and the flow insert 9, e.g. a static mixer, are insertedinto the profile during the course of deformation of the metal blank,and the profile is then pressed to form a tube-shaped semi-finishedpiece. The bead-shaped widened tube regions are finished using shapingtools, whereby the collars shown in FIG. 5 are formed. The ring disks 10are fixed in place in the collars 11, with a positive lock, and hold theflow insert 9. The longitudinal seam of the tube 1 is welded before andafter the final deformation.

FIG. 6 shows another preferred embodiment of a tube 1′ producedaccording to the invention. The tube 1′ is intended for use as a gasdistributor tube for an airbag in a vehicle, particularly for so-calledhead airbags or side airbags. This is a long, slim tube having a lengthof 1 m to 2 m, and a diameter of about 15 mm. The gas distributor tube1′ has a connector cuff 2 for a connection to a gas source, as well as aring-shaped collar 3, to which a bag, not shown, can be attached.Several exit openings 13 are arranged in a row in the longitudinaldirection.

The mantle for the gas distributor tube 1′ shown in FIG. 6, which isstraight and provided with areas having a widened cross-section, for theconnector cuff 2 and the collar 3, is punched out as a planar metalblank 4. The metal blank 4 is shown in FIG. 7. Its outside contourcorresponds to the developed view of the gas distributor tube 1′,whereby the parting plane 14 for the developed view has been laidthrough the exit openings 13. Accordingly, the lengthwise sides of themetal blank 4 each have a profile with projections 15 and back-sets 16.The projections 15 are assigned to the regions of the gas distributortube 12 having a widened cross-section, in other words the connectorcuff 2 and the ring-shaped collar 3. The back-sets 16 punched out on theedges complement one another when the metal blank 4 is deformed in tubeshape, to form the exit openings 13, and form the edges of the exitopenings 13. The width of the metal blank corresponds to the outsidediameter of the gas distributor tube 1′, multiplied by the number π.With reference to the neutral phase that runs through the wall of themantle, there is a slight excess dimension, which promotes thesubsequent defect-free longitudinal welding of the gas distributor tube1′.

The deformation of the metal blank 4 as well as the welding of thetube-shaped semi-finished piece 7 takes place analogous to the method ofprocedure described above (see FIG. 3 to 4).

The metal blank 4 can be punched out of a piece of sheet metal, e.g. azinc-plated piece of sheet steel. In this connection, it is practical toselect the length of the punched segments in such a manner that thetransitions from one punched segment to the next lie in the region ofthe back-sets 16 of the metal blank 4 that form the exit openings 13.

The tubes 1, 1′ shown in FIGS. 1 and 6 can be given a predeterminedspatial progression that corresponds to their use, by means of bending.

Alternatively, a bending deformation that shapes the work piece in thelongitudinal direction can also take place at the same time withdeformation of the metal blank 4 and/or with the subsequent pressing toform a tube-shaped semi-finished piece 7. In this way, the work piece isgiven a spatial progression adapted to the application, before thelongitudinal slit of the tube-shaped semi-finished piece 7 is weldedclosed. Preferably, the metal blank 4 is formed into a work piece havinga U-shaped cross-section, by means of bending in a forging die or edgerolling, which piece is curved in the longitudinal direction, andsubsequently is pressed to form a tube, using press die-plates whoseshaping cavity is adapted to the shape of the work piece. FIGS. 8 a and8 b show a curved gas distributor tube 1′ produced according to thisbending method. In the views shown, the exit openings 13 cannot be seen.

Segments curved in arc shape, shown in FIG. 9, can be shaped by means ofbending the gas distributor tube 1′ that has already been deformedthree-dimensionally and welded closed at the longitudinal seam.

The method according to the invention is characterized, in comparisonwith the state of the art, by a lesser number of work steps. It has theadvantage that even tubes, preferably gas distributor tubes, having asmall diameter and large exit openings on the mantle can be produced. Inparticular, tubes having an inside diameter of 12 mm or less can also beproduced according to the method according to the invention. The metalblank 4 can also have a segment having a lesser width, which forms aregion of the tube having a narrowed cross-section, after deformation ofthe metal blank, as shown in FIGS. 8 a, 8 b, and 9. The work piece isgiven a spatial progression that is adapted to the subsequent use, asearly as during the deformation of the metal blank 4. Subsequent bendingdeformation of the finished tube is not required, or can be restrictedto end segments angled off in arc shape, for example.

1. Method for the production of a metal tube, which has at least onechange in cross-section, wherein the tube mantle is punched out as aplanar metal blank (4), the outside contour of which corresponds to thedeveloped view of the tube (1, 1′), the planar metal blank (4) is formedinto a profile (5) having a U-shaped cross-section, the U-shaped profile(5) is pressed to form a tube-shaped semi-finished piece (7) that stillhas an open longitudinal slit, and the longitudinal slit, which extendswithout interruption with an essentially constant gap width over theentire length of the tube, is welded closed.
 2. Method according toclaim 1, characterized in that the metal blank (4) has segments ofdifferent width, which are connected by means of constant transitionsegments.
 3. Method according to claim 1 or 2, characterized in that themetal blank is punched out in a width that corresponds to the outsidediameter of the tube, multiplied by the number π.
 4. Method according toone of claims 1 to 3, characterized in that press die-plates (6, 6′)configured as half-shells are used for the production of the tube-shapedsemi-finished piece (7) and that the shank ends of the U-shaped profile(5) are held at a distance that forms the longitudinal slit, by means ofa tongue (8), during the shaping.
 5. Method according to one of claims 1to 4, characterized in that a welding tool, for example one controlledby an automatic welding machine, is guided along the longitudinal slitof the tube-shaped semi-finished piece (7), which follows the spatialprogression and the contour of the tube and welds the longitudinal seamclosed.
 6. Method according to one of claims 1 to 5, characterized inthat within the course of the deformation of the metal blank (4),functional elements (9) are inserted, which are fixed in place with apositive lock, by means of the wall profile, after completion of thetube (1, 1′).
 7. Method according to claim 6, characterized in thatprojections are formed on the lengthwise sides of the metal blank (4),which form an annular space for holding a functional element (9), afterdeformation to produce a tube-shaped semi-finished piece, and that thecontour forming the annular space is finished with external shapingtools.
 8. Method according to claim 6 or 7, characterized in thatprojections are formed on the lengthwise sides of the metal blank (4),which form a bead-shaped widened tube region to hold a disk (10), afterdeformation to produce a tube-shaped semi-finished piece (7), and thatthe widened tube region is pressed to form a collar (11), using shapingtools, in which the disk (10) is fixed in place with a positive lock. 9.Method according to one of claims 6 to 8, characterized in that a flowinsert (9) arranged between two support disks (10) is laid into theprofile within the course of the deformation process, and that thesupport disks are fixed in place, with a positive lock, in collars (11)that are formed during the course of the deformation of the metal blank(4), and finished using shaping tools.
 10. Method according to one ofclaims 1 to 9, characterized in that the lengthwise edges of the metalblank (4) have a profile with back-sets (16), which complement oneanother during the deformation of the metal blank (4) to form a tube(1′), to form exit openings (13) on the mantle, which are in a row inthe longitudinal direction.
 11. Method according to one of claims 1 to10, characterized in that the lengthwise edges of the metal blank (4)have a profile with projections (15), from which a collar (3) and aconnector cuff (2) are formed during the deformation of the metal blank(4) to form a tube (1′).
 12. Method according to one of claims 1 to 11,characterized in that the metal blank (4) has a segment with a lesserwidth, which forms a narrowed cross-section of the tube afterdeformation of the metal blank.
 13. Method according to one of claims 10to 12, characterized in that the metal blank (4) is punched out of apiece of sheet metal, in segments, whereby the length of the segments isselected to be such that the transitions lie in the region of theback-sets (16) on the edges of the metal blank (4) that form the exitopenings (13).
 14. Method according to one of claims 1 to 13,characterized in that the tube that has been produced from the planarmetal blank (4) and welded longitudinally is given a predeterminedspatial progression adapted to the application, by means of bending. 15.Method according to one of claims 1 to 13, characterized in that abending deformation that shapes the work piece in the longitudinaldirection takes place at the same time with deformation of the metalblank (4) and/or with the subsequent pressing to form a tube-shapedsemi-finished piece (7), and that in this way, the work piece is given aspatial progression adapted to the application, before the longitudinalslit of the tube-shaped semi-finished piece (7) is welded closed. 16.Method according to claim 15, characterized in that the metal blank (4)is deformed into a work piece having a U-shaped cross-section, by meansof bending in a forging die or edge rolling, which piece is curved inthe longitudinal direction and subsequently pressed into a tube shapeusing press die-plates (6, 6′), the shaping cavity of which is adaptedto the shape of the work piece.
 17. Method according to claim 15 or 16,characterized in that segments curved in arc shape are deformedsubsequently, by means of bending of the tube that has already beenshaped three-dimensionally and welded at the longitudinal seam.